Layer 1 protocols and technologies have evolved including Synchronous Optical Network (SONET)/Synchronous Digital Hierarchy (SDH) in the 1990s to Optical Transport Network (OTN) in the 2000s. SONET/SDH were synchronous protocols optimized for circuit switching and transmission. OTN evolved from SONET/SDH to provide transparency and support for Wavelength Division Multiplexing (WDM) as well as for optimized transmission of packet traffic. SONET, SDH, and OTN each have a rich suite of Operations, Administration, and Maintenance (OAM) functions and support for a wide range of services and applications. Conventionally, as OTN scales beyond 100G (B100G), there are emerging frameworks for Layer 1 functionality, namely Flexible OTN (FlexO or B100G) initiatives in the International Telecommunication Union (ITU) and Flex Ethernet in the Optical Internetworking Forum (OIF).
Traditionally, Ethernet rates were defined in steps of 10×, i.e., 10 Mb/s, 100 Mb/s, 1 Gb/s (GbE), etc. There is a wrinkle in this 10× progression where 40 Gb/s Ethernet (40 GbE) was defined. Today, there are various Ethernet rates defined, including rates in-between established rates. IEEE 802.3 standards group is discussing 2.5 Gb/s, 5 Gb/s, 25 Gb/s and other various odd rates. Specifically, different rates are established for different applications, such as wireless applications, data center group applications, data center interconnections, etc. There is an expectation that different Ethernet rates will continue as new high-volume applications require optimized solutions. Specifically, router/switch equipment and optical transmission equipment are evolving at different rates. There is a desire to support simple transport of n×Ethernet streams across a faster interface. IEEE historically defines Ethernet rates (Media Access Control (MAC) layer) with projects that also define the Physical (PHY)/Physical Medium Dependent (PMD) rates; the MAC rates and PMD rates are tied and defined together. To address evolution in Ethernet and dissociate the MAC/client rate from the PHY/PMD, Flexible Ethernet has been proposed. Note, as described herein, the terms Flexible Ethernet, Flex Ethernet, and FlexE can be used interchangeably.
In transport applications, FlexE can be used to match the flexibility of optical transmission equipment. Specifically, optical transmission equipment (e.g., Dense Wave Division Multiplexing (DWDM)) is evolving to support variable modulation formats, Forward Error Correction (FEC) schemes, baud rates, etc. DWDM equipment can support a variable line rate with the same hardware, relying on configuration and provisioning. FlexE is based on Ethernet constructs, e.g., 64b/66b encoding, recognizing the primary client being transported is Ethernet. Note, the current scope of FlexE is limited to interfacing applications (e.g., bonding, subrating, and channelization). However, it may be advantageous to leverage Flexible Ethernet to augment or even replace OTN and/or FlexO in some transport and switching applications.
OAM functionality is critical for operating networks, fault isolation, service and path awareness, and the like. Again, OTN provides a rich set of OAM capabilities for layer 1 circuit switching and transport applications. Ethernet also provides a rich set of OAM capabilities for layer 2 packet networking and transport applications, such as through the efforts of the Metro Ethernet Forum (MEF). However, FlexE clients (in current IA) do not have defined OAM functionality and cannot be transported and switched as a service or private line service in a provider's network.